Any chance we could convince you to review the various speakers you've owned in more detail -- either on a new thread elsewhere in AudioCircle, or on your own website? For example, I'm dying to know how the Infinity Preludes sounded to you versus others in your menagerie.
I'd also love to read a step-by-step guide for building the non-sub modules of Bob or perhaps just Roberta. I have a small listening room and two good-enough isobaric subs, but I would love to get the sound of your Bobs in my little room. Would a pair of Robertas with good subs deliver much of Bob's magic in a smaller room? (I ask because you mentioned that Bob's second midrange driver was 'probably overkill' anyway...) How much did a pair of Robertas cost for raw materials? You're not the same person as Stephen Moore who, rather like you, writes of his Beethoven-derived Phoenix speakers, "There is a special feeling when listening to the JM Labs Grand Utopia and thinking my system at home sounds so much better" ? http://home.insightbb.com/~stephenwmoore/Speakers/Linkwitz_Main.htm
Kent,
I didn't review the other speakers I've owned on my site since it is mainly a DIY dipole site. For the record though, I had the Infinity Prelude MTS at the same time as I had the Genesis V. While the Inifinity is a nice speaker, I thought the Genesis was better - more natural and open.
Not coincidentally, the Genesis is a dipole.
The best site for all dipole matters is of course
www.linkwitzlab.com. Another good one is the DIY forum at
www.htguide.com. Everything I know I stole from them.
Building your own dipole is probably the easiest project in speakerbuilding. All you need is a piece of MDF of the appropriate size, some holes for the speakers, and then a way of having the aforementioned piece of MDF point at you at the right height.
My minipoles, which I called Roberta, are a prime example of this:
The dimensions were stolen shamelessly from Dr. Linkwitz, notably his Orion speaker and his PMT1 prototype:
http://www.linkwitzlab.com/proto.htm#PMT1The panel is 30cm x 42cm MDF. The supports need to be high enough to get the tweeter at 42 inches high. They are 50mm at the top and 150 at the bottom. The overall width of the speaker with support panels is 335mm or 13 inches.
Next - drivers.
The crossover point is lower than most speakers at 1400, so you need a tweeter that can go that low. For my center minipole I use the Seas T25-02 Millenium, since I use that in my mains. Other cheaper possibilities include the Vifa XT25, Scanspeak 9500, Seas 27TDFC and I'm sure others. I have also used the Focal TC90.
The midrange driver needs to be an 8 inch with decent Xmax that can go up to 1400Hz. I use the Seas W22 in my center and the Seas L22 in my surrounds, although the L22 is marginal this high. Other alternatives are the HiVi M8a, HiVi M8n, Scan Speak 8554.
The 8 inch with high xmax is needed because the mids need to be EQed for flat response. Dipoles roll off at 6dB an octave below a certain point, which in the case of Roberta is around 350Hz.
Your next decision is how to do the crossover and EQ. I prefer active crossovers and active EQ, and the easiest way to do this is with one of the new digital crossovers like the Behringer DCX2496. You need to program in a low shelf filter for the dipole boost (18dB down to 50Hz), a notch filter for the dipole peak (-6dB at 450Hz), and (depending on mid driver) possibly a notch filter for any driver resonance peaks.
The crossover between mids and tweeter is Linkwitz Riley 24dB.
It is possible to do this with an analog active crossover and EQ, just a bit harder.
And you could go passive crossover and active EQ, which I have done on my surrounds. If you are really cheap, you can almost get away with using the bass boost of amplifier tone controls for the dipole boost.
Or SL has plans for a fully passive version of the crossover on his site.
You will need a 24dB LR crossover to the sub at about 100Hz if you are to get reasonable volume. BTW, in an ideal world you would have dipole subs too.
You should end up with a speaker that will give you a real taste of dipole sound - open, transparent and in all senses of the word boxless.
You mentioned cost. It depends which drivers you use. The full bore version using Seas Excel driver is $160 for tweeter and for the mid. The cheapest would be the HiVi M8n ($60) and the Seas 27TDFC ($30). The Behringer crossover/EQ is $350, or you could build your own I guess.
Hope this helps.
Cheers
Steve
And I'm not Stephen Moore although I admire his taste in speakers.
